Indoor cellular systems are becoming increasingly spread, as user demands for everywhere coverage are matched by the opportunity for mobile operators to offer improved services and increase traffic revenues. The owners of the building, in which the indoor cellular system is provided, also benefit from such a system, as the value of their property and their ability to attract and retain key tenants increases.
It is estimated that two thirds of all calls are made from inside a building and, with the increased demands for high data traffic capabilities, there is a growing need for improved capacity and coverage from indoor users.
An in-building cellular system offloads surrounding macro sites and ensures a higher quality of service for indoor users.
One of the basic components provided in a distributed antenna system (DAS) is the power splitter, which divides the power from a radio base station, NodeB or eNodeB for distribution to several antennas. The splitter distributes the signal equally to multiple antennas and is normally a passive component that has one input and several outputs. The splitter is an RF component which cannot amplify the input signal and splits it at the output only. By way of example, in case of a 2-way splitter, the splitter splits the input signal power into two equal output powers, whereas, in case of a 3- or 4-way splitter, the splitter splits the input signal in three and four equal output power signals, respectively. The 4-way splitter, by way of example, splits power fed at its input equally to each of the four antennas connected to the respective output port.
In FIG. 1 a splitter 10 as known in the prior art is shown in further detail. The splitter 10 comprises an input port 11 to which the total power Ptotal is fed for distribution to different output ports 12. The splitter shown in FIG. 1, a 3-way splitter, comprises three output ports 12 to which the total power Ptotal is distributed. In the splitter shown the power is equally distributed to each output port with Ptotal=P1+P2+P3 with P1=P2=P3.
This traditional splitter does not consider the traffic load at the antennas connected to the different output ports so that the power will be split independently of the number of mobile stations connected to the antennas.
Furthermore, antenna problems can cause a significant degradation of coverage in cells of the network. It is very difficult and costly for an operator to detect these antenna problems, unless they cause severe and acute radio problems. As a consequence many antenna installation problems are hidden for the operator or are mistaken for general cell plan issue, interference problem or even a problem with radio network functionality.
With the current architecture of an indoor cellular network it is not possible to optimize the power and to manage the power distribution flexibly in terms of carried traffic by each antenna. As a consequence a major part of the radio base station power is wasted in the building distributed antenna system.
Additionally, antenna problems can only be found easily, when the antenna is directly connected to the radio base station as it is the case for outdoor cellular systems. In case of an indoor cellular network, antennas are normally not directly connected to the radio base station. They are connected to the radio base station through MCM (Multi Casting Matrix) and splitters/tapers. Antennas and feeders which are connected to chain of passive components, such as splitters or tapers, cannot be detected.